C date and time functions

The C date and time functions are a group of functions in the standard library of the C programming language implementing date and time manipulation operations. They provide support for time acquisition, conversion between date formats, and formatted output to strings.

History

The format string used in strftime traces back to at least PWB/UNIX 1.0, released in 1977. Its date system command includes various formatting options. In 1989, the ANSI C standard is released including strftime and other date and time functions.

Overview of functions

The C date and time operations are defined in the header file.

	Identifier	Description
Time manipulation		computes the difference in seconds between two `time_t` values
Time manipulation		returns the current time of the system as a `time_t` value, number of seconds,. The value of the epoch is operating system dependent; 1900 and 1970 are often used. See RFC 868.
Time manipulation		returns a processor tick count associated with the process
Time manipulation		returns a calendar time based on a time base
Format conversions		converts a `struct tm` object to a textual representation
Format conversions		converts a `time_t` value to a textual representation
Format conversions		converts a `struct tm` object to custom textual representation
Format conversions		converts a string with time information to a `struct tm`
Format conversions		converts a `struct tm` object to custom wide string textual representation
Format conversions		converts a `time_t` value to calendar time expressed as Coordinated Universal Time
Format conversions		converts a `time_t` value to calendar time expressed as local time
Format conversions		converts calendar time to a `time_t` value.
Constants		number of processor clock ticks per second
Constants	`TIME_UTC`	time base for UTC
Types		broken-down calendar time type: year, month, day, hour, minute, second
Types		arithmetic time type
Types		process running time type
Types		time with seconds and nanoseconds

The and related types were originally proposed by Markus Kuhn to provide a variety of time bases, but only was accepted. The functionalities were, however, added to C++ with the release of C++20 in std::chrono.

Example

The following C source code prints the current time to the standard output stream.

include
include
include

int main

The output is:

Current time is Thu Sep 15 21:18:23 2016